1. Field of the Invention
The present invention relates to an active matrix display device and more specifically to an active matrix display device which performs signal writing through current signals.
2. Description of the Related Art
In contrast to CRT displays, flat panel display devices exemplified by liquid crystal display devices are rapidly increasing in demand because of their features of being small in thickness, light in weight, and low in power consumption. Above all, active matrix display devices, in which on pixels are electrically isolated from off pixels and a pixel switch is provided for each pixel which has a function of holding a video signal to it when it is on, have found applications in various displays, including portable information devices, because they offer good display quality with no crosstalk between adjacent pixels.
In recent years, as self-emission type displays which allow the response to be made faster and the angle of visibility to be made wider in comparison with the liquid crystal display devices, organic electroluminescence (EL) display devices have been developed vigorously. The organic EL display device contains an organic EL element as a display element and a pixel circuit adapted to supply a drive current to the display element for each pixel and performs a display operation by controlling emission brightness. As systems for supplying image information to the pixel circuit, a current-signal-based system as disclosed in, for example, U.S. Pat. No. 6,373,454 B1 and a voltage-signal-based system as disclosed in, for example, U.S. Pat. No. 6,229,506 B1 are known.
However, with a display device which performs signal supply through current signals, the capacitance of an interconnect line which performs signal supply may result in failure to perform sufficient signal supply. In particular, when the write current value is small, there arises a problem that display failures occur due to insufficient writing. In addition, for multi-degradation display, difficulties are involved in writing on the low-degradation side where the set amount of current is small, causing display failures to occur.